The invention relates to an instrument kit making it possible to achieve spinal stabilization by means of a bone anchor element of the screw type via the posterior approach or via the posterolateral approach.
The instrument kit of the invention is designed particularly, but not exclusively, for lumbar, thoracic, or indeed posterior cervical spinal osteosynthesis surgery via minimally invasive surgery or open surgery.
When anatomical dysfunctions occur in the vertebral column, bone anchors of the vertebral or pedicle screw type are put in place in the vertebrae and are connected together by link elements of the rod or plate type.
In a particular application, the invention relates to the field of single-use instrument sets, packaged in sterile manner, and comprising all of the tools necessary for performing a surgical operation of fitting pedicle screws without using additional instruments.
In the prior art, a spinal device is described in US Patent Application US2004/138662, that device being constituted by a split tube having, at its distal end, means for fastening to a screw. The distal end is hinged via a hinge making it possible to move the proximal ends of the two branches apart so as to release the head of the screw and so as to enable the tube to be removed after the screw has been implanted.
In the meaning of the present invention, the term “proximal” is used to designate the end closer to the spinal operation zone and thus the end that is further away from the operator, and the term “distal” is used to designate the end that is opposite from the spinal zone, and thus that is accessible for the operator. The screw is fastened to the “proximal” end.
International Patent Application WO2007/092870 describes another solution for a spinal device, formed by a tube having a grabber-type clamp at its proximal end.
US Patent Application US2005/0192570 proposes another embodiment of a spinal device constituted by a tube having a longitudinal slot and a split proximal end making it possible to fasten a screw to it and to release the screw by moving the proximal end apart.
Such prior art solutions that propose to release the screw by moving the proximal ends of the screw-carrier tube apart are unsatisfactory because they require sufficient space, in the zone around the screw, for enabling it to be detached. Unfortunately, in that zone, the presence of the bone portion often limits the available space, and can give rise to difficulties for releasing the tube relative to the head of the screw.
In addition, the forces that need to be transmitted for radially disengaging the proximal end of the tube relative to the head of the screw are high and transmitting them involves manipulation that is not ergonomic and that needs to be performed remotely. Releasing the screw involves actions that can also mask the intervention zone during this difficult phase of the operation.
Finally, the Applicant's international patent application WO2011/080426 describes a surgical kit for fastening vertebrae via the posterior approach or via the posterolateral approach, that kit comprising at least one vertebral or pedicle screw, and a fitting tube co-operating with said screw, that kit being characterized in that:                said fitting tube is made up of two rigid independent tubes;        on the inside face of its proximal end, each of the tubes has a shoulder of shape complementary to the shape of an indentation provided on either side of the screw head, in order to allow said screw to be taken hold of, or to be released by moving the distal ends of said tubes apart;        the kit further comprising a retractable securing insert for securing together said tubes; and        said retractable securing insert having longitudinal fastening means arranged to be dovetail shaped so as to come into engagement with complementary slideways provided in said rigid tubes.        
The various solutions proposed in the prior art suffer from a major drawback: when the surgeon exerts large forces on the tubes in order to correct the positions of the vertebrae into which the screws are engaged, the proximal ends of the tube can become detached from the screw, or, when the tube is made of a plastic material, for single-use applications, can break.